What’s the Most Muscle You Can Gain?

The fitness and supplement industries have promised improbable results for as long as they’ve existed. Here’s the truth about the limits of human muscle growth

I saw my first bodybuilding show in the early 1980s. It was an amateur contest in St. Louis, my hometown. The range of physiques on display was astounding.

One guy had the widest shoulders I’d ever seen, with deltoids that looked like twin moons in partial eclipse. Another, a compact former powerlifter competing for the first time, had muscles that seemed impossibly dense. Even the also-rans had distinct strengths and weaknesses.

The highlight, though, was a guest posing routine by Tom Platz, a pro bodybuilder with thighs that were easily the size of my waist at the time. His legs reminded me of those pictures we used to draw in grade school of cars with jet engines. It had never occurred to me that a human could pack on that much muscle.

I knew little about diet and training, and even less about genetics and steroids. All I saw was a ton of muscle, and I wanted to know how to get more. Thirty years later, I’m pretty sure I know. And it’s not at all what I expected.

Part 1: The upper limits

In The Sports Gene, author David Epstein has a definitive answer to the question of how much muscle any individual can pack onto his frame: five pounds for every pound of bone.

Unfortunately, you’d need a DEXA scan to figure out how much muscle and bone you have now, and by extension how much more you could gain if everything worked out exactly right.

Research typically tackles the question with short-term training programs, often with one group using a nutritional supplement and the other getting a placebo. Stuart Phillips, Ph.D., who has conducted many of these studies at McMaster University in Ontario, says he expects the average subject to gain 4 to 7 pounds of muscle in three months.

No matter how good the program or supplements are, he never sees average gains exceeding about a half-pound a week.

Individuals, he notes, will show more extreme results. One guy might gain 15 pounds, while another doesn’t build any measurable amount of muscle. But the average will still be around 4 to 7 pounds.

Moreover, Phillips adds, the gains in the first 12 weeks of training are a very good indication of their overall potential. “I’m not saying guys can’t put on muscle with more than 12 weeks of training, but you see a good deal of what people can do in that time. More importantly, if you’re a hardgainer in those 12 weeks, then you’re a hardgainer, period.”

To Phillips, the reason for the disparity in results—the difference between a textbook hardgainer like me and the bodybuilders on that stage—is “90 percent genetics.”

Part 2: Zygote stew

With all the tools we have to manipulate diet and training programs, and all the ways that lifestyle choices affect your physique, it’s hard to believe that genes play such an outsized role in the results. We can accept that genetics determine our height and hairlines. But our muscles?

Start with satellite cells. These are stem cells within your muscles that provide extra nuclei, giving them a more powerful growth stimulus. The only way to know how many satellite cells you have would be to take biopsies of the muscles and run sophisticated and presumably expensive tests.

That’s what researchers at the University of Alabama-Birmingham did for a 2008 study in the Journal of Applied Physiology.

They found that the relative number of satellite cells predicted who would gain the most muscle over a 16-week training program. A quarter of them didn’t gain any muscle at all in their quadriceps, while a quarter increased their quad mass by more than 50 percent.

So if nothing else, we can conclude that Tom Platz, the bodybuilder with turbines for legs, started with a ridiculous load of satellite cells.

Muscle-building potential isn’t entirely, invisibly mysterious. Sometimes you can look at someone before he starts training and see the potential.

A guy who looks like an athlete, with wide shoulders and the kind of frame that doesn’t disappear when he turns sideways, will probably look even more athletic when he’s spent some time in the weight room.

The converse is someone like me. In my teenage years even fat guys thought it was fair to make fun of my skinny arms and legs. The size and shape of those muscles is limited by the length of tendons, relative to the length of bones.

Think of your biceps. A bigger muscle belly will have a shorter tendon connecting it to the forearm. The most genetically gifted lifter will have biceps that appear to begin right at the elbow joint; when his arms are flexed, there’ll be little if any space between his upper- and lower-arm muscles.

Individual muscles aside, when we talk about building muscle, more often than not we’re also talking about gaining weight. That requires eating more than your body needs to maintain its current size, and it involves a different but equally complex set of variables.

Part 3: Weight, what?

It’s easy to gain weight if you don’t care what kind of weight you gain. But most guys who think it through will choose to do a “clean bulk”—muscle gain with minimal fat gain.

Alan Aragon, my coauthor on The Lean Muscle Diet, estimates that an entry-level lifter can gain 2 to 3 pounds of muscle mass in a month without adding much fat. An intermediate can gain 1 to 2 pounds a month, and an experienced lifter will be lucky to add a half-pound.

There’s also the “dirty bulk,” in which you lift hard and eat anything that doesn’t move fast enough to get out of your way. How much you gain during a mass overfeeding, and how much of it is muscle, depends on two key variables.

Dr. Gilbert Forbes, a pioneer in the study of body composition, showed that fat and lean tissue increase or decrease in relationship to each other. When a lean person overeats, 60 to 70 percent of the additional weight will be lean tissue. It’ll be the opposite for someone with high body fat, who’ll gain 60 to 70 percent fat and just 30 to 40 percent lean mass.

But there’s a lot of individual variation, and yet again your genes seem to be running the show.

Perhaps the greatest weight-gain experiment ever conducted began in the late 1980s at Laval University in Quebec.

The research team took 12 pairs of identical twins, all relatively lean but sedentary young males, and overfed them for 100 days. The average increase was 18 pounds—about two-thirds lean tissue and one-third fat—but the range was from 9 to 29 pounds. The number-one predictor of how much an individual gained was how much his twin gained. (Genes also determined where they added the fat.)

Why didn’t everyone gain the same amount of weight? In a 2014 study in the International Journal of Obesity, the researchers showed that those with the highest VO2 max (a measure of aerobic fitness) and the highest percentage of Type I muscle fibers (the ones responsible for long-duration, low-intensity work) gained the least weight, with the highest proportion of lean mass.

On the flip side, the men with the highest percentage of Type IIA muscle fibers—the ones that produce speed, strength, and power—gained the most weight, and the largest proportion of fat. (Find out Why Dwayne “The Rock” Johnson is Technically Obese.)

The same applied to men whose muscles had the most glycolytic potential, a measure of their ability to produce energy when they’re moving too fast to use their aerobic energy system. For most of us, the glycolytic system is what we use for all-out efforts lasting 30 to 60 seconds (although well-trained athletes can use it for up to two minutes).

Thus, the men who were wired for long-distance sports gained the least weight when overfed, and gained the lowest percentage of fat.

That’s the good news for hardgainers. And the men who were predisposed to be better at lifting or sprinting not only gained weight easily, they gained a higher proportion of fat.

If you’d told the young, skinny me all of this 30 years ago, as I watched those bodybuilders flex and strut and flex some more, I wouldn’t have believed you. How could these huge guys be so lean if their ability to put on weight also predisposed them to gain excess fat?

The obvious answer is because they trained hard to gain muscle and then dieted hard to lose fat. The subjects in the Laval University study were all sedentary. We can’t say what the results would’ve been if they’d lifted during the 100 days of overfeeding, only that they probably would’ve gained less fat and more muscle.

But there was another factor in the bodybuilders’ results that I didn’t account for at the time.

Part 4: Shot class

The first studies linking synthetic testosterone to increased muscle and strength were published in the early 1940s. But it wasn’t until the mid 1950s that anabolic drugs were clearly and permanently linked to sports performance.

Americans dominated weightlifting in the early postwar years. But in 1953, the Soviet Union won its first world championship, and in 1954 a doctor for the Soviet team admitted to his American counterpart that his athletes were injecting testosterone. The American doctor, John Ziegler, went on to develop Dianabol, the first oral steroid, and Winstrol, an injectable.

You know the rest of the story. By the 1960s steroids were pervasive in strength and power sports, from the Olympics to the NFL. They were especially important to the new and fast-growing sports of powerlifting and bodybuilding. But at the time only the insiders in sports, fitness, and exercise science understood just how important they were.

The fitness industry, where I was just beginning to learn my way around, had a vested interest in obscuring the line where human potential ended and anabolic drugs took over.

Who would read about Mr. Olympia’s sleeve-busting biceps workout if it included a list of the illegal, expensive, and potentially dangerous drugs he took to build arms equal in circumference to his skull?

The article might include a list of the nutritional supplements he took, if those supplements happened to be sold by the same company that published the magazine. But mostly it would focus on exercises you saw every day in the local gym, only with bigger weights and veinier arms.

In sports, athletes were able to exploit a generation of sportswriters who didn’t train and had no idea what could be achieved without drugs. My favorite example is a Baseball America article from 2002. Under the subhead “Raw Talent Takes Time” is this paragraph about how Jose Canseco transformed himself from a middling prospect to a superstar:

“But 1985 saw a different Canseco. Already considered less than focused, he matured dramatically after coming to grips with his mother’s death early in the previous season. He also added 30 pounds in offseason workouts.”

The highlighted part wasn’t italicized in the original. It was just a sentence dropped into an article describing Canseco’s amazing leap from hitting 15 homers in the lower levels of the minor leagues in 1984 to hitting 36 in the upper levels in ’85, and then to becoming American League Rookie of the Year in ’86 and MVP in ’88.

You’d think that by 2002 no sportswriter would’ve been naïve about the effects of steroids. Canseco, who had recently retired, was already talking about his own steroid use, and claimed most ballplayers were doing the same thing. But then as now, the dramatic narrative of athletes triumphing over adversity is a lot more entertaining if you leave out the chemistry.

So what exactly do steroids add to conventional training?

In a landmark 1996 study in the New England Journal of Medicine, men who received testosterone injections gained twice as much strength and several times as much lean mass as men who did the exact same training program and followed the exact same diet.

In 10 weeks the juiced subjects gained 13 pounds of lean mass, compared to 4 pounds for those who got a placebo. All the subjects had lifting experience.

Phillips regards these results as a clear indication of the difference between training with or without steroids. An average guy can hope to gain 4 to 7 pounds of muscle in 10 to 12 weeks of serious training, and that’s only if he’s either new to lifting or returning from a layoff. The more experienced and dedicated you are, the less you can gain.

It’s possible for an individual to gain more, just as it’s possible for someone to gain nothing, or perhaps even lose some size, despite working as hard and eating as well as he can. But neither of those is likely.

So if you hear about a training program or see an ad for a supplement promising results that exceed these norms, you can be sure of one thing: Someone is just making shit up.

(And for ways to transform your body sans steroids, check out The Better Man Project. It’s a jam-packed user’s guide to every aspect of a man’s life, with more than 2,000 body hacks and fitness, nutrition, health, and sex secrets.)

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